Methods and apparatuses for multiple access in a wireless communication network using DCT-OFDM

ABSTRACT

The present invention provides an advantageous transmitter apparatus and associated method, for generating a Single-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal for transmission. These transmit-side innovations include circuit configuration and signal processing methods for mapping K u  “input subcarriers” to N “output subcarriers,” where the “output subcarriers” are some or all of the subcarriers defined for the SC-DCT OFDM signal. In one or more embodiments, K u  is less than N, and the mapping is based on advantageous DCT/IDCT precoding. The present invention additionally or alternatively includes advantageous frequency-selective mapping, and further provides a corresponding receiver apparatus and associated method, for receiving and de-mapping the SC-DCT OFDM signals contemplated herein.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/913,119, filed on Oct. 27, 2010, now U.S. Pat. No. 8,693,571, whichclaims priority to U.S. Provisional Patent Application No. 61/313,346filed on Mar. 12, 2010, all of which are hereby incorporated byreference herein in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to wireless communicationnetworks, and particularly relates to methods and apparatuses providingmultiple-access in wireless communication networks based on DCT-OFDM(Discrete Cosine Transform Orthogonal Frequency Division Multiplex).

BACKGROUND

OFDM based on Discrete Fourier Transform (DFT) processing is a popularmodulation approach in developing and planned wireless communicationsystems, such as 3GPP LTE, IEEE WiMAX 802.16x, IEEE WiFi 802.11x, etc.DFT-based modulation provides efficient and practical channelequalization algorithms, when used for the transmission of multi-carriersignals, like the OFDM signals used in LTE and LTE-Advanced.Furthermore, multiple access solutions that allow flexible resourceallocation (e.g., Orthogonal Frequency Division Multiple Access orOFDMA) can be implemented in conjunction with the use of DFT-based andother OFDM signals structures.

However, the OFDM signal is characterized by large fluctuations of itspower envelope that result in occasional spikes in the power of thesignal—for example, such signals are characterized by having arelatively high Peak-to-Average-Power-Ratio (PAPR) or high “CubicMetric” (CM). The large power fluctuations in high PAPR/CM signalsimpose significant design requirements on the radiofrequency (RF) poweramplifier (amplifier chains) used to transmit OFDM signals. Inparticular, the large power fluctuations require the RF Pas to beoperated with significant back-off, to have sufficient margin foraccommodating the power peaks in the OFDM signal. More generally, theoverall transmit signal chain must be “dimensioned” in one or moresenses, to handle the worst-case power peaks of the OFDM signal.

For energy, cost, or space critical designs (e.g., mobile devices) thepower back-off margins required by DFT-OFDM lead to an inefficientsolution. Therefore, modifications to the standard OFDM system have beenintroduced, to obtain systems with roughly the same advantages ofDFT-OFDM over single carrier systems, but with more compressed signaldynamics. The two most popular techniques are Distributed Single CarrierOFDMA (sometimes also called B-IFDMA) and Localized Single Carrier(LOC-SC) OFDMA, also referred to as DFTS-OFDM. LOC-SC-OFDMA has beenadopted for 3GPP LTE, to improve the efficiency of uplink transmissions.

In both LOC/DIST-SC-OFDMA, the Inverse DFT (IDFT) modulator at thetransmitter is preceded by a standard DFT precoder. The two techniquesdiffer in the way the outputs from the DFT precoder are mapped to theinputs on the IDFT. Inverse processing is correspondingly performed atthe receiver side, and linear equalization techniques can be performedin the same way as for conventional OFDM/OFDMA. As a furtheralternative, researchers have investigated new modulation systems basedon the use of Discrete Cosine Transform (DCT) processing. See, e.g., P.Tang, N. C. Beaulieu, “A Comparison of DCT-Based OFDM and DFT-Based OFDMin Frequency Offset and Fading Channels,” IEEE 2006.

Further work has touched on the use of DCT-based transmission“precoding” in the OFDM context, in the interest of improving systemperformance through, e.g., lower Bit Error Rates (BERs). See, e.g., deFein, C. and Fagan, A. D., “Precoded OFDM—An Idea Whose Time Has Come,”ISSC 2004, Belfast. Additional work on precoding in the context ofDCT-based OFDM appears in, e.g., Wang, Zhengdao and Giannakis, Georgios,“Linearly Precoded or Coded OFDM against Wireless Channel Fades?” ThirdIEEE Signals Processing Workshop, Taiwan, 2001.

Broadly, with DCT-based OFDM, the transmitter employs a DCT (or,equivalently, an IDCT) for modulation processing. Compared toconventional DFT-based OFDM systems equalization in the DCT-OFDM contextis more complex. However, DCT-based OFDM systems retain the attractivechannel diagonalization properties of DFT-OFDM, based on employing asymmetric Cyclic Prefix (CP) and a pre-filter at the receiver. See,e.g., N. Al-Dhahir, H. Minn, S. Satish, “Optimum DCT-Based MulticarrierTransceivers for Frequency-Selective Channels,” IEEE 2006.

While DCT-based OFDM offers a number of promising characteristics, theunderlying signals used in an a DCT-OFDM system still experiencepotentially large envelope fluctuations that are difficult to handlewithin the practical limits of hardware. Furthermore, there appears tobe significant work remaining in developing efficient multiple accesstechniques that allow the co-scheduling of multiple users, while stilloffering an advantageously low PAPR/CM.

SUMMARY

The present invention provides an advantageous transmitter apparatus andassociated method, for generating a Single-Carrier Discrete CosineTransform (SC-DCT) OFDM signal for transmission. These transmit-sideinnovations include circuit configuration and signal processing methodsfor mapping K_(u) “input subcarriers” to N “output subcarriers,” wherethe “output subcarriers” are some or all of the subcarriers defined forthe SC-DCT OFDM signal. In one or more embodiments, K_(u) is less thanN, and the mapping is based on advantageous DCT/IDCT precoding. Thepresent invention additionally or alternatively includes advantageousfrequency-selective mapping, and further provides a correspondingreceiver apparatus and associated method, for receiving and de-mappingthe SC-DCT OFDM signals contemplated herein.

In one embodiment, the present invention provides a transmitter circuitconfigured to generate an SC-DCT OFDM signal for transmission. Thetransmitter circuit includes a signal processing chain configured to mapK_(u) input subcarriers to N output subcarriers, according to theformula N=2^(S)K_(u). Here, S indicates the integer number of DCTprecoder stages included in series within the signal processing chain,where S≥1.

The signal processing chain of the transmitter circuit includes: aserial-to-parallel converter configured to generate the K_(u) inputsubcarriers according to a series of information symbols to betransmitted; a cyclic prefix or zero padding circuit configured to add acyclic prefix or zero padding to the N output subcarriers, for input toa parallel-to-serial converter that is configured to form the SC-DCTOFDM signal; and one or more series DCT precoder stages between theserial-to-parallel converter and the cyclic prefix or a zero paddingcircuit.

Each such DCT precoder stage is configured to generate 2M outputsubcarriers from M input subcarriers, and to map the M input subcarriersto even-numbered or odd-numbered ones of the 2M output subcarriers, independence on an even/odd shift control signal applied to the stage, andeach such stage comprising a DCT circuit followed by an IDCT circuit.Further, a first one of the DCT precoder stages takes the K_(u)subcarriers as its M input subcarriers, and a last one of the DCTprecoder stages provides the N output subcarriers as its 2M outputsubcarriers.

In another embodiment, the present invention provides a method ofgenerating an SC-DCT OFDM signal for transmission. The method includesforming a parallel vector of K_(u) input subcarriers from a series ofinformation symbols to be transmitted, and mapping the K_(u) inputsubcarriers to N output subcarriers by passing the K_(u) inputsubcarriers through one or more DCT precoder stages. Here, N=2^(S)K_(u),and S (S≥1) indicates the integer number of series DCT precoder stages.Further, the method includes inserting a cyclic prefix or a zero paddinginto the N output subcarriers and subsequently converting the N outputsubcarriers into a serial signal, for generating the SC-DCT OFDM signalfor transmission.

As for mapping according to the method, the mapping done in each DCTprecoder stage comprises passing M input subcarriers through a DCTfunction followed by an IDCT function, to generate 2M outputsubcarriers. The M input subcarriers are mapped to even or odd ones ofthe 2M output subcarriers, in dependence on an even/odd shift controlsignal. In this regard, M=K_(u) for a first DCT precoder stage and 2M=Nfor a last DCT precoder stage.

In a further embodiment, the present invention provides a method ofgenerating an SC-DCT OFDM signal for transmission, where the methodincludes forming a parallel vector of K_(u) input subcarriers from aseries of information symbols to be transmitted, and mapping the K_(u)input subcarriers to N output subcarriers. That mapping is accomplishedby passing the K_(u) input subcarriers through a mapping circuit and anInverse (IDCT) circuit of size N, wherein K_(u)<N.

In particular, the K_(u) subcarriers are mapped on a frequency-selectivebasis to said N output subcarriers, based on identifying preferredsubcarrier frequencies. For example, channel state information from aremote receiver targeted by the SC-DCT OFDM signal can be used to guidethe frequency-selective mapping, such as to select those subcarriershaving more favorable fading and/or interference characteristics. Themethod further includes inserting a cyclic prefix or a zero padding intothe N output subcarriers and subsequently converting the N outputsubcarriers into a serial signal, for generating the SC-DCT OFDM signalfor transmission.

In yet another embodiment, the present invention provides a receivercircuit configured to process a received SC-DCT OFDM signal. Thereceiver circuit includes a signal processing chain configured to de-mapN input subcarriers from the received SC-DCT OFDM signal to K_(u) outputsubcarriers, according to the formula K_(u)=N/2^(S), wherein S indicatesthe integer number of DCT decoder stages included in series within thesignal processing chain. (Note that S≥1.) The signal processing chainalso includes a pre-processing circuit that is configured to remove acyclic prefix from the N input subcarriers, in advance of thede-mapping.

As part of its decoding configuration, the signal processing chainincludes one or more series DCT decoder stages following thepre-processing circuit. Each such stage is configured to generate Moutput subcarriers from 2M input subcarriers, by mapping even-numberedor odd-numbered ones of the 2M input subcarriers as said M outputcarriers, in dependence on an even/odd shift control signal applied tothe stage. In accordance with this configuration, each DCT decoder stagecomprises a DCT circuit followed by an IDCT circuit. Thus, a first oneof the DCT decoder stages takes the N input subcarriers as its 2M inputsubcarriers, and a last one of the DCT decoder stages provides the K_(u)output subcarriers as its M output subcarriers.

Still further, in another embodiment the present invention provides amethod for use in a receiver circuit configured to process a receivedSC-DCT OFDM signal. The method includes removing a cyclic prefix from Ninput subcarriers from the received SC-DCT OFDM signal, and de-mappingthe N input subcarriers from the received SC-DCT OFDM signal to K_(u)output subcarriers, after removing said cyclic prefix, according to theformula K_(u)=N/2^(S). Here, S indicates the integer number of DCTdecoder stages included in series within a signal processing chain ofthe receiver circuit, where S≥1.

According to the method, the de-mapping includes, in each of one or moreseries DCT decoder stages included in the receiver circuit, generating Moutput subcarriers from 2M input subcarriers, based on mappingeven-numbered or odd-numbered ones of the 2M input subcarriers as said Moutput carriers, in dependence on a an even/odd shift control signalapplied to the stage, and further comprising generating said M outputcarriers based on performing a DCT on the 2M input subcarriers, followedby performing an IDCT on the results obtained from said DCT.

Further, while this disclosure uses LTE Advanced as an example context,it should be understood that the present invention has broaderapplicability. For example, the present invention has applicability tofuture evolutions of other systems, including WCDMA, CDMA, WiMax, UMB,etc. More generally, the present invention is not limited to the abovebrief summary of features and advantages. Indeed, those skilled in theart will recognize additional features and advantages upon reading thefollowing detailed description, and upon viewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a first radio apparatusconfigured to generate and transmit an SC-DCT OFDM signal as taughtherein, and a second radio apparatus configured to receive and processthat signal.

FIGS. 2-4 are block diagrams of example embodiments of transmit andreceive signal processing chains, such as can be used in the radioapparatuses of FIG. 1.

FIGS. 5 and 6A/B are block diagrams of one embodiment of the DCTprecoder and decoder stages, respectively, as are used in the signalprocessing chains depicted in FIG. 4.

FIGS. 7 and 8 are logic flow diagrams, illustrating one embodiment ofcomplementary transmitter and receiver methods of SC-DCT OFDM signalprocessing, as taught herein.

FIGS. 9 and 10 are diagrams of one embodiment of direct implementationof DCT/IDCT processing, to avoid DCT/IDCT computations.

FIGS. 11 and 12 are block diagrams of one embodiment of complementaryradio devices, configured to transmit an SC-DCT OFDM signal (as in FIG.11) and to receive an SC-DCT OFDM signal (as in FIG. 12).

DETAILED DESCRIPTION

FIG. 1 illustrates a first radio apparatus 10 (“Device 1”) that includestransmit processing circuits 12 configured to cooperate with an OFDMtransmitter 14, for transmission of an SC-DCT OFDM signal from one ormore transmit antennas 16. The radio apparatus 10 is configured togenerate SC-DCT OFDM signals according to any one or more of theembodiments taught herein. In complementary fashion, FIG. 1 furtherdepicts a second radio apparatus 20 (“Device 2”) that includes receiverprocessing circuits 22 configured to receive and process SC-DCT OFDMsignals, as received at the radio apparatus 20 via its OFDM receiver 24and associated antenna(s) 26.

As part of the signal processing carried out in the system of FIG. 1(i.e., at or between the two radio apparatuses 10 and 20), anadvantageous embodiment of the DCT-related processing is based on theorthogonal DCT matrix, expressed as:

$\begin{matrix}{{C\left( {l,m} \right)} = \left\{ {\begin{matrix}{{\sqrt{\frac{2}{N}}{\cos\left( \frac{\left( {l - 1} \right)\left( {{2m} - 1} \right)\pi}{2N} \right)}},} & {{1 \leq l},{m \leq N},{l \neq 1}} \\{\sqrt{\frac{1}{N}},} & {l = 1}\end{matrix}.} \right.} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$

With the above DCT structure in mind, FIG. 2 illustrates one embodimentcontemplated herein for SC-DCT OFDM signal generation, transmission, andcorresponding reception and processing. In at least one embodiment, thetransmit-side processing circuitry illustrated in FIG. 2 provides forDCT-OFDMA, where multiple users are supported based on selectivelymapping each user to a different subset of the defined or available Nsubcarriers within the overall SC-DCT OFDM signal.

In FIG. 2, a given serial stream of information symbols (e.g.,associated with a given user) is processed by a transmit signalprocessing chain 30, which is implemented, for example, in the transmitprocessing circuits 12 of the radio apparatus 10 depicted in FIG. 1. Theinput signal (serial symbol stream) is parallelized via aserial-to-parallel (S/P) converter 32, making it a length K_(u) symbolvector—note that successive blocks of K_(u) symbols from the inputinformation stream are used to generate successive length-K_(u) symbolvectors, for transmission via the SC-DCT OFDM signal being generated bythe transmit signal processing chain 30. That signal includes a total ofN defined or otherwise available subcarriers, at spaced apart narrowbandcarrier frequencies (as is generally understood for OFDM), and thelength-K_(u) symbol vector is mapped to K_(u) of the N subcarriers,where, for one or more embodiments herein, K_(u) is less than N.

Note that the other subcarriers are, in at least one embodiment,assigned zero (“0”) or no-signal values. Thus, where the radio apparatus10 is one of multiple user terminals or other devices transmitting onthe uplink (UL) to the radio apparatus 20 serving as a network basestation, it will be understood that different such devices may usedifferent K_(u) subsets of the N available subcarriers. Thus, the set ofselected K_(u) subcarriers used by a given user is, according to one ormore embodiments taught herein, assigned by a scheduling function. Forexample, by properly choosing the scheduled subcarriers it is possibleto focus the signal energy on the most convenient or favorable portionsof the wireless channel, i.e., typically the subcarrier where thechannel has large energy.

The illustrated transmit signal processing chain 30 includes, beyond theS/P converter 32, a mapping circuit 34 that maps the K_(u) subcarriersto particular ones of the N subcarriers of the OFDM signal—in thiscontext, the K_(u) subcarriers are referred to as “input” subcarriers,as they are the ones being mapped, and the N subcarriers are referred toas the “output” subcarriers, as they are the actual subcarriersavailable for use in the transmitted OFDM signal.

In any case, the mapping circuit 34 is followed by an IDCT circuit 36(of size N), which applies an Inverse Discrete Cosine Transform to theK_(u) subcarriers. The size N output from the IDCT circuit 36 includesthe mapped K_(u) subcarriers with the remaining (N−K_(u)) subcarriersset, e.g., to zero. A CP/ZP circuit 38 inserts a cyclic prefix (CP) or azero padding (ZP). Note that at least one embodiment of the CP/ZPcircuit 38 adds a CP and, optionally, a cyclic suffix (CS). Also, notethat certain design issues may be considered in terms of decidingwhether to use CP insertion or ZP insertion. For example, CP insertioneffectively diagonalizes the propagation channel and thereby simplifiesequalization processing at the receiver, although prefiltering generallyis required. In contrast, equalization is more complex when ZP is used,but prefiltering generally is not needed.

After CP or ZP insertion, a parallel-to-serial (P/S) converter 40converts the signal to a serial stream. The serial stream is input tothe OFDM transmitter circuit 14, for D/A conversion, modulation to thecarrier/subcarrier frequencies, amplification, etc., and transmission asthe SC-DCT OFDM signal.

Thus, one method taught herein is the generation of an SC-DCT OFDMsignal for transmission, based on: forming a parallel vector of K_(u)input subcarriers from a series of information symbols to betransmitted; and mapping the K_(u) input subcarriers to N outputsubcarriers through a mapping circuit 34 and an Inverse DCT (IDCT)circuit 36 of size N, wherein N>K_(u). In particular, wherein themapping is performed on a frequency-selective basis, based onidentifying preferred subcarrier frequencies. That is, the IDCT circuit36 maps the K_(u) parallel information symbols to the inputs of the IDCTcircuit 36, which produces N output subcarriers.

On the receive-side, one sees an example receive signal processing chain50, which, for example, is implemented within the receiver processingcircuits 22 that are depicted for the second radio apparatus 20 inFIG. 1. The SC-DCT OFDM signal propagates from the transmit antenna(s)16 of the first radio apparatus 10 and is received on the antenna(s) 26of the second radio apparatus 20, where it is initially processed in theOFDM receiver 24 (e.g., filtered, downconverted/digitized).

The receive signal processing chain further includes a CP/ZP removalcircuit 52, which also may be configured as a prefilter; a size N DCTcircuit 54; a demapping circuit 56, to de-map the K_(u) subcarriers ofinterest from the N subcarriers; an equalization (EQ) circuit 58 tooperate on the K_(u) subcarriers; and a parallel-to-serial (P/S)converter 60, to output a serialized version of the equalized signalfrom the EQ circuit 58. It will be understood that a base station orother node intended for receiving and processing signals from multipleremote transmitters will include (at least functionally) multiplereceive signal processing chains 50, for processing the signals fromdifferent transmitters. Alternatively, the receive signal processingchain 50 can be sized or otherwise structured to process multiple setsof K_(u) subcarriers from the received SC-DCT OFDM signal.

FIG. 3 depicts another embodiment, which presents a solution referred toas “LOC-SC-DCT-OFDM” (Localized Single Carrier DCT based OFDM). In thiscase, the user signal of length K_(u) symbols is first precoded througha DCT precoder circuit 42 of length K_(u), and then mapped to the IDCTmodulator circuit 36. The mapped precoded information symbols output bythe DCT precoder 42 are, for example, mapped to adjacent subcarriers, intypical SC fashion.

In at least one embodiment, a method of generating a LOC-SC-DCT OFDMsignal for transmission comprises converting a number K_(u) ofinformation symbols into a parallel vector of K_(u) information symbols,and precoding the parallel K_(u) information symbols in a DiscreteCosine Transform (DCT) precoder, to create K_(u) precoded informationsymbols. The method further includes mapping the K_(u) precodedinformation symbols to K_(u) selected inputs of an Inverse DCT (IDCT)modulator and correspondingly generating K_(u) mapped subcarriers fromamong N output subcarriers from the IDCT modulator. Still further, themethod includes inserting a cyclic prefix (CP) or a zero padding (ZP)into the N subcarriers, and converting the N subcarriers into a serialstream for transmission as the LOC-SC-DCT signal. Note that in at leastone such embodiment, generating the K_(u) mapped subcarriers from amongN output subcarriers from the IDCT modulator comprises generating K_(u)consecutively-mapped subcarriers from among N output subcarriers fromthe IDCT modulator.

Such transmit-side precoding results in the receive signal processingchain 50 including an extra component, as compared to the embodiment ofFIG. 2. Namely, an IDCT circuit 62 of size K_(u), positioned after theequalizer 58. As compared to the embodiment of FIG. 2, the embodiment ofFIG. 3 provides a basis for a multiple access (MA) scheme that allowsmore limited scheduling flexibility, given that adjacent mapping of theK_(u) subcarriers is required for best CM performance. That is, wherethe frequency-selective mapping used in the transmit processing chain 30of FIG. 2 may use non-contiguous mapping of the K_(u) subcarriers to theN available subcarriers, the embodiment of FIG. 3 can be constrained touse consecutive mapping to maximize CM performance.

FIG. 4 illustrates yet another embodiment of the present invention.Here, the transmit signal processing chain 30 is modified to include oneor more DCT precoder stages 44 (e.g., 44-1 through 44-r) that areserially chained to implement a form of the DCT precoding and mappingpreviously described. Correspondingly, the illustrated receive signalprocessing chain 50 includes an embodiment of the previously introducedOFDM receiver 24, for receiving the OFDM signal(s) transmitted by thetransmit signal processing chain 30.

The illustrated receive signal processing chain 50 further includes aCP/ZP removal circuit 52. If the CP/ZP insertion circuit 38 of thetransmit signal processing chain 30 is configured to insert a CP, thenthe CP/ZP removal circuit 52 is configured to remove the CP from thereceived signal. Conversely, if the CP/ZP insertion circuit 38 isconfigured to use zero padding—i.e., to insert a ZP rather than aCP—then the CP/ZP removal circuit 52 is configured to remove the ZP fromthe received signal.

As earlier noted, one advantage of CP insertion on the transmit side isthe advantage of simpler equalization on the receive side. Thatadvantage is partially offset by the need for pre-filtering of thereceived signal when CP insertion is used. Thus, the receive signalprocessing chain 50 illustrates a pre-filter circuit 53, which isused/implemented in the case that CP insertion is used on the transmitside. In such configurations, the pre-filter circuit 53 is configured toprovide the necessary received signal pre-filtering. If ZP insertion isused on the transmit side, pre-filtering need not be implemented.

Following the CP/ZP removal and (possible) pre-filtering, one sees aseries of DCT decoder stages 64. In general, the receive signalprocessing chain 50 includes the same number of DCT decoder stages 64 asDCT precoder stages 44 used in the transmit signal processing chain 30.Here, one sees DCT decoder stages 64-1 through 64-r, corresponding toDCT precoder stages 44-1 through 44-r on the transmit side. Also, notethat the first DCT decoder stage 64-1 generally includes an EQ circuit65, such as depicted in FIG. 6A.

The use of CP insertion on the transmit side provides channeldiagonalization and attendant simplification of the equalizationprocessing implemented in the eq. circuit 65, while the use of ZPgenerally requires more complex equalization process, whileadvantageously eliminating the need for pre-filtering. In any case,those of ordinary skill in the art will appreciate that the eq. circuit65 may be configured to implement an equalization matrix and processingcircuit that forms linear combinations of the input (received signal),where the resultant combined (signals) exhibit reduced inter-carrierinterference.

In the embodiment of FIG. 4, which may be referred to asDIST-SC-DCT-OFDM (Distributed Single Carrier DCT OFDM), the number ofscheduled subcarriers is related to the number of defined or availablesubcarriers as N=2^(S)K_(u), where S is an integer that indicates thenumber of DCT precoding stages 44, as explained below.

Each DCT precoding stage 44 on the transmit side doubles the number ofgenerated subcarriers and maps the signal only on even or oddsubcarriers according to a SHIFT(s)={0;1} flag, where s is the precoderindex. Therefore, only the subcarriers indexed as offset+k*2^(S) (withk=0 . . . K_(u); offset={0 . . . −2^(S)−1}) carry the transmittedsignal, while the other subcarriers do not carry energy. The value ofthe variable offset is determined by the values of SHIFT(s).Corresponding decoding steps are performed at the receiver side, where,as noted, the first DCT decoder stage 64-1 includes or is associatedwith equalization processing, as provided by the eq. circuit 65.

Each DCT precoder stage 44 (and corresponding DCT decoder stage 64) isobtained from a combination of down-sampled DCT/IDCT processing andsubcarrier mapping, as shown in FIG. 5. Particularly, FIG. 5 depicts aDCT precoder stage 44 as comprising an input DCT circuit 70 thatreceives an Mx1 input vector. The output from the DCT circuit 70 servesas the input to a size 2M IDCT circuit 72, which provides 2M outputsubcarriers. The complementary, opposite arrangement is shown in FIGS.6A and 6B, for the receive-side processing, wherein a DCT circuit 80receives 2M input subcarriers, with its output fed to a size 2M IDCTcircuit 82 that outputs M output subcarriers. (Note that DCT decoderstage 64-1 receives a time-domain input signal, and outputssubcarriers.)

Further, the switches 74/76 in FIGS. 5 and 84/86 in FIGS. 6A and 6Bcorrespond to the even-odd shifting control done responsive to theSHIFT(s) signals applied to each stage. For clarity, FIG. 6A depicts thefirst DCT decoder stage 64-1 within the receive signal processing chain,with the eq. circuit 65 integrated within its signal processing stages.FIG. 6B correspondingly illustrates any one of the succeeding DCTdecoder stages 64-2, . . . , 64-r.

The embodiment of FIGS. 4-6A/B may offer less scheduling flexibility, ascompared to the embodiments of FIGS. 2 and 3, for example, because thescheduled K_(u) subcarriers are distributed over the whole bandwidth ofthe N subcarriers, albeit according to the even or odd mapping. On theother hand, this embodiment offers excellent CM performance. (It can beanalytically shown that the output signal in this embodiment preservesthe CM of the input signal.)

Further, with the embodiment of FIG. 4 in mind, FIGS. 7 and 8 illustrateexample, complementary transmit-side and receive-side methods that arerespectively implemented by the radio apparatuses 10 and 12 20 of FIG.1, and particularly according to the signal processing chains 30 and 50shown in FIG. 4.

FIG. 7 broadly depicts a method 700 for generating the types of SC-DCTOFDM transmit signals contemplated in the embodiment depicted in FIG. 4.It will be understood that the transmit processing circuits 12 and OFDMtransmitter 14 of the radio apparatus 10 are configured (e.g., viasoftware, hardware, or both) to carry out the illustrated method, whichincludes forming a parallel vector of K_(u) input subcarriers (Block702). These K_(u) “subcarriers” represent the parallelized symbolstreams formed by converting, e.g., blocks of a serial transmitinformation stream into corresponding parallel symbol vectors.

The method 700 continues with mapping the K_(u) input subcarriers to Noutput subcarriers, wherein the mapping is performed in one or more DCTprecoder stages (Block 704). Here, the “output” subcarriers representthe actual subcarriers available for use in the SC-DCT OFDM transmitsignal to be generated. Thus, the process takes an ongoing serialtransmit information stream and converts it into a succession of symbolvectors, each having K_(u) information symbols, and where each suchsymbol vector is referred to as K_(u) “input subcarriers.” In turn,those K_(u) input subcarriers are mapped to N particular ones of theactual subcarriers comprising the OFDM signal structure.

In particular, the mapping is done using advantageously constructed andconfigured DCT precoders, as will be detailed later herein. The methodcontinues with inserting a CP or ZP and converting the N outputsubcarriers to serial form, which is then amplified, etc., andtransmitted as the SC-DCT OFDM signal (Block 706).

FIG. 8 illustrates a corresponding receiver method 800, which isimplemented within the radio apparatus 20 of FIG. 1, in one or moreembodiments taught herein. According to the method, the receiverprocessing circuits 22 of the radio apparatus 20 are configured toprocess a received SC-DCT OFDM signal, based on removing a CP or ZP fromN input subcarriers from the received SC-DCT OFDM signal (Block 802).

The method continues with de-mapping the N input subcarriers from thereceived SC-DCT OFDM signal to K_(u) output subcarriers, after removingsaid CP or ZP (Block 804). The de-mapping is done according to theformula K_(u)=N/2^(S), where S indicates the integer number of DCTdecoder stages included in series within a signal processing chain ofthe receiver circuit 22 (S≥1). The contemplated de-mapping includes, ineach of one or more series DCT decoder stages included in the receivercircuits 22, generating M output subcarriers from 2M input subcarriers.

In particular, such processing is based on mapping even-numbered orodd-numbered ones of the 2M input subcarriers as said M output carriers,in dependence on a an even/odd shift control signal applied to thestage, and further comprising generating said M output carriers based onperforming a DCT on the 2M input subcarriers, followed by performing anIDCT on the results obtained from said DCT. In any case, the methodcontinues with further received signal processing (Block 806), such asdecoding or otherwise extracting the originally-transmitted informationsymbols, for data or control processing at the radio apparatus 20.

Accordingly, in one embodiment, the present invention comprises atransmitter circuit (e.g., transmitter processing circuits 12)configured to generate an SC-DCT OFDM signal for transmission. Thetransmitter circuit includes a signal processing chain 30 configured tomap K_(u) input subcarriers to N output subcarriers, according to theformula N=2^(S)K_(u). The term S indicates the integer number of DCTprecoder stages 44 included in series within the signal processing chain30, wherein S≥1.

The signal processing chain 30 includes a serial-to-parallel converter32 configured to receive a series of K_(u) information symbols and tocorrespondingly generate a parallel set of K_(u) output informationsymbols—e.g., a vector of K_(u) output information symbols, fortransmission. A CP/ZP circuit 38 is configured to add a CP or ZP to theN output subcarriers, for input to a parallel-to-serial (P/S) converter40 that is configured to form the SC-DCT OFDM signal. Further, as noted,the signal processing chain 30 further includes one or more series DCTprecoder stages 44 between the serial-to-parallel converter 32 and theCP/ZP circuit 38.

Each such stage 44 is configured to generate 2M output subcarriers fromM input subcarriers, and to map the M input subcarriers to even-numberedor odd-numbered ones of the 2M output subcarriers, in dependence on aneven/odd shift control signal applied to the stage 44. (The transmitprocessing circuits 12 will be understood to include, for example, ashift control circuit configured to generate the shift control signals.)Further, as shown in FIG. 5, each such DCT precoder stage 44 comprises aDCT circuit 70 followed by an IDCT circuit 72. With this arrangement, afirst one of the DCT precoder stages 44-1 takes the K_(u) subcarriers asits M input subcarriers, and a last one of the DCT precoder stages 44-rprovides the N output subcarriers as its 2M output subcarriers.

In at least one embodiment, there is a plurality of said signalprocessing chains 30, each associated with different series ofinformation symbols to be transmitted, and a shift control circuit thatis configured to generate even/odd shift control signals for each saidsignal processing chain 30, such that different patterns of even or oddsubcarrier mapping are used between the different signal processingchains 30. In at least one such embodiment, the shift control circuit isconfigured to generate the different patterns of even or odd subcarriermapping in consideration of the number of DCT precoder stages 44included in each signal processing chain 30.

Further, in at least one such embodiment, the shift control circuit isincluded in a multiple-access scheduling circuit—which, again, isimplemented functionally within the transmit processing circuits 12, inone or more example embodiments—that is configured to determine thenumber of subcarriers allocated to different users, and to control theshifting behaviors of each corresponding signal processing chain 30, todifferentiate between the different users.

Accordingly, a method is taught herein comprising mapping a plurality ofdifferent sets of K_(u) input subcarriers according to differenteven/odd shift control signals having different patterns of even/oddshifting, to differentiate the different sets of K_(u) inputsubcarriers. In particular, in one embodiment, the method includesgenerating the different even/odd shift control signals as part of amultiple-access scheduling method that uses the different patterns ofeven/odd shifting to differentiate between individual receivers—e.g.,multiple radio apparatuses 12 10 —being targeted by SC-DCT OFDM signaltransmissions.

Still further, in at least one embodiment, at least one DCT precoderstage 44 in the signal processing chain 30 comprises a direct-mappingDCT precoder stage 44 that is configured to form the 2M outputsubcarriers by taking the M input subcarriers as a length-M orderedsequence and outputting a length-2M output vector that includes theoriginal ordered sequence interspersed with a time-reversed and mirroredversion of the original ordered sequence. Such direct-mapping is basedon, for example, the direct-mapping DCT precoder stage 44 beingconfigured to negate or not negate the time-reversed mirrored version ofthe original ordered sequence included in the length-2M output vector,in dependence on the even/odd shift control signal applied to thedirect-mapping DCT precoder stage 44.

Likewise, referring again to FIG. 4, the present invention provides areceiver circuit configured to process a received SC-DCT OFDM signal.Such a receiver circuit is functionally implemented within the receiverprocessing circuits 22, for example, and includes a signal processingchain 50 that is configured to de-map N input subcarriers from thereceived SC-DCT OFDM signal to K_(u) output subcarriers, according tothe formula K_(u)=N/2^(S). Here, the S term indicates the integer numberof DCT decoder stages 64 included in series within the signal processingchain 50, wherein S≥1, and wherein the signal processing chain 50includes a pre-processing circuit 52 that is configured to remove a CPor ZP from N input subcarriers in advance of de-mapping.

Further, the signal processing chain 50 further includes the previouslymentioned one or more series DCT decoder stages 64 following thepre-processing circuit 52. Each such stage 64 is configured to generateM output subcarriers from 2M input subcarriers, by mapping even-numberedor odd-numbered ones of the 2M input subcarriers as said M outputcarriers. Such mapping is performed in dependence on a an even/odd shiftcontrol signal applied to the stage 64, and each such stage 64 comprisesa DCT circuit 80 followed by an IDCT circuit 82 (such as is shown in theexample of FIG. 6). With this arrangement, a first one of the DCTdecoder stages 64-1 takes the N input subcarriers as its 2M inputsubcarriers, and a last one of the DCT decoder stages 64-r provides theK_(u) output subcarriers as its M output subcarriers.

In at least one such embodiment, at least one of the DCT decoder stages64 in the signal processing chain comprises a direct-mapping DCT decoderstage that is configured to form the M output subcarriers by selecting alength-M ordered sequence from the 2M input subcarriers, which are knownto be formed as a length-2M ordered sequence the length-M orderedsequence interspersed with a time-reversed and mirrored version of thelength-M ordered sequence.

Also, regardless of whether direct mapping is or is not used, at leastone embodiment of the receiver circuit includes a parallel-to-serialconverter circuit 60 that is configured to convert the K_(u) outputsubcarriers into a corresponding serial stream, and a processing circuit(e.g., within the receive processing circuits 22) that is configured toobtain or otherwise process the information symbols of interest from theserial stream. Such symbols represent data and/or control signaling.

As for example details of the above direct mapping, the presentinvention advantageously recognizes that certain properties of theDIST-SC-DCT-OFDM scheme can be exploited in the implementation of theDCT precoder and decoder stages 44 and 64, respectively. In particular,it is contemplated herein that the DCT precoder and decoder stages 44and 64 may be implemented in such a way as to avoid explicitcalculations of the DCT/IDCT. Notably, the thus-avoided DCT/IDCTcomputations may well be the most computationally intensive operationsat the transmitter or receiver. The alternative (“direct”)implementations of the DCT precoder and decoder stages 44 and 64 areshown in FIGS. 9 and 10, respectively. Note that the direct-determinedoutput sequence of FIG. 9 is or is not based on the negated,time-reversed mirrored versions of the original ordered input sequence,based on the state of the even/odd shift control signal applied to thedirect-mapping DCT precoder stage 44.

With the above examples in mind, those skilled in the art willappreciate that the present invention provides a number of advantages.Those advantages include these non-limiting examples: (1) an effectivemultiple access method that trades scheduling flexibility for signaldynamics compression and where, even in case of full bandwidthallocation, the embodiments of FIGS. 2, 3, and 4 provide reduced CM/PAPRcompared to conventional DCT-OFDM; and (2) the embodiments of FIGS. 9and 10 provide significant computational simplifications.

With these example advantages in mind, FIG. 11 illustrates an exampleradio device 90, which may be configured, for example, as a transmittingnode in a wireless communication network. In one example, the device 90comprises a mobile terminal configured for operation in an LTE,LTE-Advanced, or other type of wireless communication network. Thedevice 90 may be configured, for example, consistent with the radioapparatus 10 introduced in FIG. 1 and discussed at length herein. Tothat end, the device 90 includes communication and control circuits 92(e.g., fixed or programmable digital processing circuitry), includingreceive/transmit control and processing circuits 94, which areassociated with transceiver circuits 96 that include one or moretransmit signal processing chains 98. These chains 98 are, for example,implemented like the transmit signal processing chain 30 depicted inFIG. 4, for example. As such, the device 90 transmits an SC-DCT OFDMsignal from its antenna(s) 100, consistent with the teachings herein.

Correspondingly, FIG. 12 illustrates an example radio device 110, whichmay be configured, for example, as a transmitting node in a wirelesscommunication network. In one example, the device 110 comprises a basestation (e.g., eNodeB or eNB) configured for operation in an LTE,LTE-Advanced, or other type of wireless communication network. Thedevice 110 may be configured, for example, consistent with the radioapparatus 20 introduced in FIG. 1 and discussed at length herein. Moreparticularly, in one or more embodiments in this context, the device 110is configured to receive and process SC-DCT OFDM signals from aplurality of devices 90.

To that end, the device 110 includes communication and control circuits112 (e.g., fixed or programmable digital processing circuitry),including transmitter/receiver processing and control circuits 114,which are associated with transceiver circuits 116 that include one ormore receiver signal processing chains 118. These chains 118 are, forexample, implemented like the receive signal processing chain 50depicted in FIG. 4, for example. As such, the device 110 receives SC-DCTOFDM signals on its antenna(s) 120, consistent with the teachingsherein.

Note, too, that in keeping with the MA techniques described herein, thedevice 110 may control or otherwise configure multiple devices 90 to usedifferent even/odd shift patterns in the DCT precoder stages 44 includedin their transmit signal processing chains 98. The assignment ofdifferent shifting patterns to different devices 90 reduces interferencebetween the SC-DCT OFDM signals transmitted on the shared uplink bythose devices 90.

Of course, the example illustrations of FIGS. 11 and 12, and the otherillustrations are not limiting. Modifications and other embodiments ofthe disclosed invention(s) will come to mind to one skilled in the arthaving the benefit of the teachings presented in the foregoingdescriptions and the associated drawings. Therefore, it is to beunderstood that the invention(s) is/are not to be limited to thespecific embodiments disclosed and that modifications and otherembodiments are intended to be included within the scope of thisdisclosure. Although specific terms may be employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation.

What is claimed is:
 1. A transmitter circuit configured to generate aSingle-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal fortransmission, said transmitter circuit comprising: a signal processingchain configured to map K_(u) input subcarriers to N output subcarriers,according to the formula N=2^(S)K_(u), wherein S indicates the integernumber of DCT precoder stages included in series within the signalprocessing chain, wherein S≥1, and wherein said signal processing chainincludes a serial-to-parallel converter configured to generate the K_(u)input subcarriers according to a series of information symbols to betransmitted, a prefix or padding circuit configured to add a cyclicprefix or a zero padding to the N output subcarriers, for input to aparallel-to-serial converter that is configured to form the SC-DCT OFDMsignal; and wherein said signal processing chain further includes one ormore series DCT precoder stages between the serial-to-parallel converterand the prefix or padding circuit, each such stage configured togenerate 2M output subcarriers from M input subcarriers, and to map theM input subcarriers to even-numbered or odd-numbered ones of the 2Moutput subcarriers, in dependence on a an even/odd shift control signalapplied to the stage, and each such stage comprising a DCT circuitfollowed by an IDCT circuit; and wherein a first one of the DCT precoderstages takes the K_(u) subcarriers as its M input subcarriers, and alast one of the DCT precoder stages provides the N output subcarriers asits 2M output subcarriers.
 2. The transmitter circuit of claim 1,wherein there is a plurality of said signal processing chains, eachassociated with different series of information symbols to betransmitted, and a shift control circuit that is configured to generateeven/odd shift control signals for each said signal processing chain,such that orthogonal patterns of even or odd subcarrier mapping are usedbetween the different signal processing chains.
 3. The transmittercircuit of claim 1, wherein at least one DCT precoder stage in thesignal processing chain comprises a direct-mapping DCT precoder stagethat is configured to form the 2M output subcarriers by taking the Minput subcarriers as a length-M ordered sequence and outputting alength-2M output vector that includes the original ordered sequenceinterspersed with a time-reversed and mirrored version of the originalordered sequence.
 4. The transmitter circuit of claim 1, wherein S>1. 5.The transmitter circuit of claim 2, wherein the shift control circuit isconfigured to generate the different patterns of even or odd subcarriermapping in consideration of the number of DCT precoder stages includedin each signal processing chain.
 6. The transmitter circuit of claim 2,wherein the shift control circuit is included in a multiple-accessscheduling circuit that is configured to determine the number ofsubcarriers allocated to different users, and to control the shiftingbehaviors of each corresponding signal processing chain, todifferentiate between the different users.
 7. The transmitter circuit ofclaim 3, wherein the direct-mapping DCT precoder stage is configured tonegate or not negate the time-reversed mirrored version of the originalordered sequence included in the length-2M output vector, in dependenceon the even/odd shift control signal applied to the direct-mapping DCTprecoder stage.
 8. A method of generating a Single-Carrier DiscreteCosine Transform (SC-DCT) OFDM signal for transmission, said methodcomprising: forming a parallel vector of K_(u) input subcarriers from aseries of information symbols to be transmitted; mapping the K_(u) inputsubcarriers to N output subcarriers by passing the K_(u) inputsubcarriers through one or more DCT precoder stages, whereinN=2^(S)K_(u), and S (S≥1) indicates the integer number of series DCTprecoder stages; and inserting a cyclic prefix or a zero padding intothe N output subcarriers and subsequently converting the N outputsubcarriers into a serial signal, for generating the SC-DCT OFDM signalfor transmission; and wherein mapping in each DCT precoder stagecomprises passing M input subcarriers through a DCT function followed byan IDCT function, to generate 2M output subcarriers, wherein the M inputsubcarriers are mapped to even or odd ones of the 2M output subcarriers,in dependence on a an even/odd shift control signal, and further whereinM=K_(u) for a first DCT precoder stage and 2M=N for a last DCT precoderstage.
 9. The method of claim 8, further comprising mapping a pluralityof different sets of K_(u) input subcarriers according to differenteven/odd shift control signals having different patterns of even/oddshifting, to differentiate the different sets of K_(u) inputsubcarriers.
 10. The method of claim 8, further comprising using directmapping in at least one DCT precoder stage, wherein said direct mappingforms the 2M output subcarriers for the given stage by taking the Minput subcarriers as a length-M ordered sequence and outputting alength-2M output vector that includes the original ordered sequenceinterspersed with a time-reversed and mirrored version of the originalordered sequence.
 11. The method of claim 9, further comprisinggenerating the different even/odd shift control signals in considerationof the number of DCT precoder stages used for mapping each set of K_(u)input subcarriers.
 12. The method of claim 9, further comprisinggenerating the different even/odd shift control signals as part of amultiple-access scheduling method that uses the different patterns ofeven/odd shifting to differentiate between individual receivers beingtargeted by SC-DCT OFDM signal transmissions.
 13. The method of claim10, further comprising negating or not negating the time-reversedmirrored version of the original ordered sequence included in thelength-2M output vector, in dependence on the even/odd shift controlsignal applied to the stage.
 14. A receiver circuit configured toprocess a received Single-Carrier Discrete Cosine Transform (SC-DCT)OFDM signal, said receiver circuit comprising: a signal processing chainconfigured to de-map N input subcarriers from the received SC-DCT OFDMsignal to K_(u) output subcarriers, according to the formulaK_(u)=N/2^(S), wherein S indicates the integer number of DCT decoderstages included in series within the signal processing chain, whereinS≥1, and wherein said signal processing chain includes a pre-processingcircuit configured to remove a cyclic prefix or zero padding from Ninput subcarriers in advance of de-mapping; wherein said signalprocessing chain further includes one or more series DCT decoder stagesfollowing the pre-processing circuit, each such stage configured togenerate M output subcarriers from 2M input subcarriers, by mappingeven-numbered or odd-numbered ones of the 2M input subcarriers as said Moutput carriers, in dependence on a an even/odd shift control signalapplied to the stage, and each such stage comprising a DCT circuitfollowed by an IDCT circuit; and wherein a first one of the DCT decoderstages takes the N input subcarriers as its 2M input subcarriers, and alast one of the DCT decoder stages provides the K_(u) output subcarriersas its M output subcarriers.
 15. The receiver circuit of claim 14,wherein at least one DCT decoder stage in the signal processing chaincomprises a direct-mapping DCT decoder stage that is configured to formthe M output subcarriers by selecting a length-M ordered sequence fromthe 2M input subcarriers, which are known to be formed as a length-2Mordered sequence of the length-M ordered sequence interspersed with atime-reversed and mirrored version of the length-M ordered sequence. 16.The receiver circuit of claim 14, further comprising aparallel-to-serial converter circuit configured to convert the K_(u)output subcarriers into a corresponding serial stream, and a processingcircuit configured to obtain information symbols of interest from theserial stream.
 17. The receiver circuit of claim 14, wherein S>1.
 18. Amethod for use in a receiver circuit configured to process a receivedSingle-Carrier Discrete Cosine Transform (SC-DCT) OFDM signal, saidmethod comprising: removing a cyclic prefix or zero padding from N inputsubcarriers from the received SC-DCT OFDM signal; de-mapping said Ninput subcarriers from the received SC-DCT OFDM signal to K_(u) outputsubcarriers, after removing said cyclic prefix or zero padding,according to the formula K_(u)=N/2^(S), wherein S indicates the integernumber of DCT decoder stages included in series within a signalprocessing chain of the receiver circuit, wherein S≥1; and wherein saidde-mapping includes, in each of one or more series DCT decoder stagesincluded in the receiver circuit, generating M output subcarriers from2M input subcarriers, based on mapping even-numbered or odd-numberedones of the 2M input subcarriers as said M output carriers, independence on a an even/odd shift control signal applied to the stage,and further comprising generating said M output carriers based onperforming a DCT on the 2M input subcarriers, followed by performing anIDCT on the results obtained from said DCT.
 19. The method of claim 18,further comprising, in at least one said DCT decoder stage in the signalprocessing chain, implementing a direct de-mapping, based on forming theM output subcarriers by selecting a length-M ordered sequence from the2M input subcarriers, which are known to be formed as a length-2Mordered sequence of the length-M ordered sequence interspersed with atime-reversed and mirrored version of the length-M ordered sequence. 20.The method of claim 18, further comprising converting the K_(u) outputsubcarriers into a corresponding serial stream, and obtaininginformation symbols of interest from the serial stream.
 21. The methodof claim 18, wherein S>1.